As all of you know, diversity is a huge factor in successful SEO. So although I've had success using only Web 2.0 and authority backlinks to my sites, I've been using another technique to give it that extra push - guest posting through Fiverr. This is definitely more of a miss than hit strategy, as so many of the blogs on there are complete shit. But always message the seller asking to see the site first and check it for spam/age. It only costs a couple of bucks but it can make a huge difference.